The mixing of viscous fluids has historically been a difficult task. Present methods of mixing such fluids often result in inadequate mixing and are time-consuming and energy consumptive.
One of the more common viscous fluids which must be mixed is paint. Homeowners and painters are all too familiar with the task of mixing paint.
Probably the most common method of mixing fluid such as paint involves the user opening the container, inserting a stir stick or rod and rotating or moving the stick about the container. This method is tiring, requiring tremendous effort to move the stir stick through the viscous fluid. Because of this, individuals often give up and stop mixing long before the paint is adequately mixed. Further, even if the individual moves the stir stick for a long period of time, there is no guarantee that the paint is thoroughly mixed, rather than simply moved about the container.
Many mechanisms have been proposed for mixing these fluids and reducing the manual labor associated with the same. These mechanisms have all suffered from at least one of several drawbacks: users have difficulty in using the device because of its complexity or size, the device inadequately mixes the fluid, the device mixes too slowly, the device does not break up or "disperse" clumped semi-solids in the fluid, and/or the users have a difficult time cleaning up the device after using it. As one example, these prior methods of mixing are generally inadequate for the purpose of mixing hard to mix materials such as additives and tints which must be thoroughly distributed in homogenous fashion to produce the desired end product. Other problems associated with these mixers are that they often introduce air into the fluid (which, in the case of paint and other coating materials is detrimental, for example, when the material is to be sprayed with a sprayer), they do not trap globules/particles which do not go into solution, and many of the mixing devices may damage the container in which the fluid is being mixed, causing the fluid to leak from the container or parts of the damaged container to enter the material being mixed.
One example of such a mechanized mixing device is essentially a "screw" or auger type device. An example of such a device is illustrated in U.S. Pat. No. 4,538,922 to Johnson. This device is not particularly effective in mixing such fluids, as it imparts little velocity to the fluid. Further, the device does not disperse clumped material in the fluid, but simply pushes it around the container.
Another method for mixing paint comprises shaking the paint in a closed container. This can be done by hand, or by expensive motor-driven shakers. In either instance, the mixing is time consuming and often not complete. Because the shaking occurs with the container closed, little air space is available within the container for the fluid therein to move about. Therefore, the shaking often tends to move the fluid very little within the container, with the result being ineffective mixing.
Several devices have been developed for mixing paint which comprise devices for connection to drills. For example, U.S. Pat. No. 4,893,941 to Wayte discloses a mixing device which comprises a circular disc having vanes connected thereto. The apparatus is rotated by connecting a drill to a shaft which is connected to the disc. This device suffers from drawbacks. First, the limited number of vanes does not provide for thorough mixing. Second, because the bottom disc is contiguous, no fluid is drawn through the device from the bottom. It is often critical that fluid from the bottom of the container be drawn upwardly when mixing viscous fluids, since this is where the heaviest of the fluids separate prior to mixing.
U.S. Pat. No. 3,733,645 to Seiler discloses a paint mixing and roller mounting apparatus comprising a star-shaped attachment. This apparatus is not effective in mixing paint, as it does not draw the fluid from the top and bottom of the container. Instead, the paddle-like construction of the device simply causes the fluid to be circulated around the device.
U.S. Pat. No. 1,765,386 to Wait discloses yet another device for mixing liquids. This device is wholly unacceptable, as it must be used in conjunction with a diverter plate located in the container to achieve adequate mixing. Use of the diverter plate would either require its installation into a paint container before being filled, which would increase the cost of paint to the consumer, or require that the consumer somehow install the device into a full paint container.
An inexpensive method for mixing viscous fluids in a quick and effective manner is needed.